1. Field of Invention
This invention relates generally to the field of interconnecting broadband antennas with detection or transmission electronics and, more particularly, to baluns and other devices for effecting such interconnections.
Financial support from the SETI Institute, made possible by the Paul G. Allen Foundation, is gratefully acknowledged.
2. Description of the Prior Art
Many antennas generate balanced signals across their input terminals requiring the inclusion of a balun between the terminals and an amplifier, detector or other electronics that typically require unbalanced input. A “balun” is basically an impedance transformer designed to couple a balanced transmission circuit and an unbalanced transmission circuit. The impedance transformation can be performed by a variety of well-known techniques, but the conversion between a balanced mode and an unbalanced mode typically requires special techniques. See, for example, “Antenna Engineering Handbook, Third Edition,” Richard C. Johnson (Ed.) (McGraw-Hill Publishing, 1993), especially Chapter 43, “Impedance Matching and Broadbanding,” by David F. Bowman and Section 43-6, pp. 43-23 to 43-27 and references cited. The contents of Chapter 43 is incorporated herein by reference.
Our discussion and description will chiefly focus on the detection of weak signals as typically required in the field of radio astronomy. However, this is by way of illustration and not limitation as other applications of the present devices and techniques, including applications for the transmission of signals through an antenna, will be apparent to those having ordinary skills in the art.
In addition to connecting and impedance matching the balanced signals received at the input terminals of an antenna with unbalanced detection electronics, it is also important that the signals be delivered to the amplifiers with as little loss as possible. Thus, it is advantageous to have the amplifiers (and cryogenic devices in some applications) located as close to the antenna terminals as feasible, and to locate these devices so as to cause as little disruption as feasible with the performance of the antenna. Space is often quite limited in the regions of antennas near the input terminals where electronics can be located, so a compact design for baluns and interconnects is advantageous. Therefore, a need exists in the art for balun and interconnection devices and techniques that permit the connection of balanced signals received at the input terminals of an antenna with unbalanced electronic devices located in close proximity to the input terminals, while avoiding substantial signal loss and avoiding substantial interference with the performance of the antenna.